Online Help for Python Assignment and Homework

1. Introduction Programming Language Python

2. What is Scripting Language? A scripting language is a “wrapper” language that integrates OS functions. • The interpreter is a layer of software logic between your code and the computer hardware on your machine. Wiki Says: • The “program” has an executable form that the computer can use directly to execute the instructions. • The same program in its human-readable source code form, from which executable programs are derived (e.g., compiled) • Python is scripting language, fast and dynamic. • Python is called ‘scripting language’ because of it’s scalable interpreter, but actually it is much more than that

3. What is Python? Python is a high-level programming language which is:  Interpreted: Python is processed at runtime by the interpreter. (Next Slide)  Interactive: You can use a Python prompt and interact with the interpreter directly to write your programs.  Object-Oriented: Python supports Object-Oriented technique of programming.  Beginner’s Language: Python is a great language for the beginner-level programmers and supports the development of a wide range of applications. 8/22/201

4. Languages • Some influential ones: • FORTRAN • science / engineering • COBOL • business data • LISP • logic and AI • BASIC • a simple language

5. Programming basics • code or source code: The sequence of instructions in a program. • syntax: The set of legal structures and commands that can be used in a particular programming language. • output: The messages printed to the user by a program. • console: The text box onto which output is printed. • Some source code editors pop up the console as an external window, and others contain their own console window.

6. compile execute source code Hello.java byte code Hello.class output interpret source code Hello.py output Compiling and interpreting • Many languages require you to compile (translate) your program into a form that the machine understands. • Python is instead directly interpreted into machine instructions.

7. Expressions • expression: A data value or set of operations to compute a value. Examples: 1 + 4 * 3 42 • Arithmetic operators we will use: • + - * / addition, subtraction/negation, multiplication, division • % modulus, a.k.a. remainder • ** exponentiation • precedence: Order in which operations are computed. • * / % ** have a higher precedence than + -1 + 3 * 4 is 13 • Parentheses can be used to force a certain order of evaluation.(1 + 3) * 4 is 16

8. Integer division • When we divide integers with / , the quotient is also an integer. 3 52 4 ) 14 27 ) 1425 12135 2 75 54 21 • More examples: • 35 / 5 is 7 • 84 / 10 is 8 • 156 / 100 is 1 • The % operator computes the remainder from a division of integers. 3 43 4 ) 14 5 ) 218 1220 2 18 15 3

9. Real numbers • Python can also manipulate real numbers. • Examples: 6.022-15.999742.02.143e17 • The operators +-*/% **() all work for real numbers. • The / produces an exact answer: 15.0 / 2.0 is 7.5 • The same rules of precedence also apply to real numbers:Evaluate () before */% before +- • When integers and reals are mixed, the result is a real number. • Example: 1 / 2.0 is 0.5 • The conversion occurs on a per-operator basis. • 7 / 3 * 1.2 + 3 / 2 • 2 * 1.2 + 3 / 2 • 2.4 + 3 / 2 • 2.4 + 1 • 3.4

10. print • print : Produces text output on the console. • Syntax: print "Message" print Expression • Prints the given text message or expression value on the console, and moves the cursor down to the next line. print Item1, Item2, ..., ItemN • Prints several messages and/or expressions on the same line. • Examples: print "Hello, world!" age = 45 print "You have", 65 - age, "years until retirement" Output: Hello, world! You have 20 years until retirement

11. input • input : Reads a number from user input. • You can assign (store) the result of input into a variable. • Example: age = input("How old are you? ") print "Your age is", age print "You have", 65 - age, "years until retirement" Output: How old are you? 53 Your age is 53 You have 12 years until retirement • Exercise: Write a Python program that prompts the user for his/her amount of money, then reports how many Nintendo Wiis the person can afford, and how much more money he/she will need to afford an additional Wii.

12. The for loop • for loop: Repeats a set of statements over a group of values. • Syntax: for variableName in groupOfValues: statements • We indent the statements to be repeated with tabs or spaces. • variableName gives a name to each value, so you can refer to it in the statements. • groupOfValues can be a range of integers, specified with the range function. • Example: for x in range(1, 6): print x, "squared is", x * x Output: 1 squared is 1 2 squared is 4 3 squared is 9 4 squared is 16 5 squared is 25

13. Cumulative loops • Some loops incrementally compute a value that is initialized outside the loop. This is sometimes called a cumulative sum. sum = 0 for i in range(1, 11): sum = sum + (i * i) print "sum of first 10 squares is", sum Output: sum of first 10 squares is 385 • Exercise: Write a Python program that computes the factorial of an integer.

14. if • if statement: Executes a group of statements only if a certain condition is true. Otherwise, the statements are skipped. • Syntax: if condition: statements • Example: gpa = 3.4 if gpa > 2.0: print "Your application is accepted."

15. if/else • if/else statement: Executes one block of statements if a certain condition is True, and a second block of statements if it is False. • Syntax: if condition: statements else: statements • Example: gpa = 1.4 if gpa > 2.0: print "Welcome to Mars University!" else: print "Your application is denied." • Multiple conditions can be chained with elif ("else if"): if condition: statements elif condition: statements else: statements

16. while • while loop: Executes a group of statements as long as a condition is True. • good for indefinite loops (repeat an unknown number of times) • Syntax: while condition: statements • Example: number = 1 while number < 200: print number, number = number * 2 • Output: 1 2 4 8 16 32 64 128

17. File processing • Many programs handle data, which often comes from files. • Reading the entire contents of a file: variableName = open("filename").read() Example: file_text = open("bankaccount.txt").read()

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